Our long-term objective is to understand how chemicals are detected in the peripheral sense organ, how the information is processed in the brain to recognize chemicals, and how the brain directs appropriate behavioral responses. These processes are essential for animals to survive and continue their species. Without a functional olfactory system, animals would have difficulty detecting food sources, predators, prey, mating partners, or noxious chemicals in the environment. In humans, a sense of smell is important for a variety of reasons, from enjoying a meal, to detecting harmful gas leakage. Although mammalian odorant receptors were cloned over 10 years ago, little is known how different odorant molecules interact with odorant receptors. In this proposed research project, we intend to identify a set of odorant receptors that recognize particular odorants and to identify amino acids and motifs in the odorant receptors that determine odorant binding. We propose three specific aims: (1): To establish a novel method to identify a set of odorant receptors that recognize particular odorants in mice, and to identify a set of odorant receptors that recognize particular odorants. (2): To create and analyze model mice for in vivo analysis of odorant receptor functions in the olfactory epithelium and in the olfactory bulb of the brain. (3): To develop a method to measure odorant receptor activation by observing b-arrestin2 localization and to identify of specific domains and amino acid residues that direct odorant binding to odorant receptors. We will first develop and use a novel method to identify multiple odorant receptors that recognize particular aliphatic odorants in mice, by combining optical imaging in the olfactory bulb, retrograde tracing, and cloning of odorant receptors from single olfactory sensory neurons using an improved single-cell RT-PCR method. Using the information gained in Specific Aim 1, we will next create transgenic mouse lines to genetically mark specific olfactory sensory neurons that express particular odorant receptors as well as axons that originate from them with green fluorescent protein (GFP). We will use these mice to analyze functions of odorant receptors by performing functional imaging experiments in the olfactory bulb as well as in single olfactory sensory neurons. Finally, we plan to develop an alternative method to measure odorant receptor activation by observing localization of b-arrestin2-GFP fusion proteins in HEK293 cells. By using this heterologous expression system or other methods, we plan to analyze domains and amino acids in the odorant receptors that determine odorant binding.